In the progress of information-oriented society, information leakage is increasingly becoming problematic. Specifically, technical development for preventing information leakage of paper media appears to be urgently required.
Japanese Patent No. 2938338 (Patent Document 1) discloses a two-dimensional code technology to attach binary data as an image to printed patter. This image is obtained by coding data in a two-dimensional matrix form. In this technology, positions of the code are detected by utilizing locating markers attached to the image, and code information is, after having been printed, read to decode the two dimensional image.
Japanese Patent No. 4348381 (Patent Document 2) discloses a technology to encrypt printed items. This technology is achieved by regularly converting image values of an area subject to encryption. Further, an image scanner detects the locating markers disposed at the time of encryption to specify the positions of the encrypted area so as to perform a decrypting process.
Japanese Laid-open Patent Publication No. 2009-232129 (Patent Document 3) discloses a technology to encrypt an image by dividing an image into plural blocks and scrambling the divided blocks. In this technology, boundary markers each indicating a boundary of the blocks are generated, and the generated boundary markers are embedded in the encrypted image so as to detect the position of each of the divided blocks of the degraded image. Note that the image captured by an apparatus such as a camera that images an encrypted image includes image degradation such as image blur due to camera shaking. Japanese Patent Application No. 2010-062694 (Patent Document 4) discloses a technology to eliminate parts having the above-described image degradation from the captured image. More specifically, the technology disclosed in Patent Document 4 identifies the degrees of the image blur based on the edge features of the locating markers to eliminate the blurred image.
In the rolling shutter system of a complementary metal-oxide semiconductor (CMOS) sensor such as digital still cameras, an image acquisition time for imaging a sheet of an image differs in each line. Hence, the degrees of camera shaking differ in each of imaged areas. Further, the sheet of the image may partially include out-of-focus areas due to three-dimensional distortion. Such a sheet of the image that partially includes image blur or image wobble is determined as being inappropriate for decoding, and will not be employed for the decoding process. Accordingly, a longer waiting time may be required for performing the decoding process until the image having no degradation is acquired. In this technology, it may be inevitable to decode the image having degradation areas when reduction in the waiting time is required. As a result, the information to be read may result in degraded information.